1. Field of the Invention
The present invention relates to a toner used in image formation by an electrostatic process, such as a copying machine, a facsimile machine and a printer, and an image forming apparatus and a process cartridge using the toner.
2. Description of the Related Art
In an image forming apparatus utilizing an electrophotographic system, a toner image is formed on a photoconductor through charging the surface of an image bearing member (hereinafter referred to as a “photoconductor” or “electrophotographic conductor”) with a discharged electrical change, exposing the surface of the charged photoconductor to form a latent electrostatic image, and developing the latent electrostatic image formed on the surface of the photoconductor by supplying a toner. The developing is carried out using a developing unit arranged in the image forming apparatus, and the toner contained in a toner container is replenished to the developing unit to compensate for toner consumption.
Recently, high and accurate reproducibility of image to be formed has come to be demanded. For this reason, toner with small particle size is used to meet this demand. However, toner with a small particle size has the problem that the powder mobility of the toner is reduced, causing incomplete replenishment by creating a snow-cave like pocket when a screw is used to supply the toner. In addition, toner particles are attached to the screw and the like to cause clogging by the toner.
Instead of monochromic images, full-color images are in greater demand in the market. To produce glossy full-color images with good quality, chromatic colorant needs to be finely dispersed within the toner to reduce the softening point of a binder resin. However, low-molecular-mass or crystallized organic pigment or dye is used as the chromatic colorant, causing deterioration of the cohesive properties of the toner so as to be more difficult of quantitative replenishment of the toner.
Recently, image forming apparatuses have tended to become smaller and its processing speed has tended to become faster. Such a high speed image forming apparatus requires a large amount of toner to be replenished, resulting in the larger size of a toner container. Further, a reliable replenishing performance is required. Coincidentally, for the reduction of the size of the overall image forming apparatus, downsizing of a fixing unit is given. For example, silicone oil or the like has been used to improve the releasing properties of the fixing unit, but the removal of a silicone oil tank has been required as the tank prevents the reduction of size. Instead of providing the releasing properties to the fixing unit, an approach to mix a releasing agent such as wax in a toner to provide the releasing properties to the toner has been used to enable a reduction in the size of the apparatus. Additionally, the toner container may be arranged away from the developing unit to reduce the size of the image forming apparatus. For this reason, a toner replenishing system utilizing a powder pump has been used to efficiently and stably replenish the toner from a separate toner container installed in the development means.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2004-037911 discloses an image forming apparatus wherein an air supply path from an air outlet of an air pump to an air connection hole being a confluence part between a path and a toner sending tube in a toner supply path is arranged above the bottom position of the path and the toner sending tube in the graviatation direction.
Furthermore, JP-A No. 2002-087592 discloses a powder transfer pump, which comprises a stator with a through hole and a rotor arranged in the through hole, wherein the powder is transferred from an inlet side of the through hole to an outlet side of the through hole by means of the rotor rotation, and an agitator is provided so that the powder discharged from the outlet of the through hole is agitated by the agitator.
However, even with the use of powder transfer pumps disclosed in the above-mentioned applications, it is difficult in the toner supply system utilizing a powder pump to achieve smooth toner replenishment with a toner utilizing a soft binder resin and containing low-molecular-mass or crystallized organic pigment or dye as chromatic colorant as well as a releasing agent. In addition, even if it is possible, there are still image failure problems such as occurrences of white dots and deteriorated image density as the toner must go through under various stresses in the toner replenishment path.